1. Field of the Invention
This invention concerns air bag systems and more particularly arrangements to form air deployment openings in an interior trim structure behind which an air bag receptacle is stored.
2. Description of the Prior Art
A folded air bag is usually stowed in a receptacle mounted behind a trim piece in the passenger compartment of the vehicle equipped with the air bag.
In some designs, the trim structure is formed with a smooth, uninterrupted decorative covering layer overlying an air bag deployment opening, and an opening must be formed in the covering layer by severing of the covering layer in a pattern forming the deployment opening.
This severing step must be accomplished within a very short time after initiation of the air bag deployment sequence so as to not retard and thus adversely affect proper deployment of the air bag as it is inflated by its inflation device. The air bag inflator device acts extremely rapidly to generate a large volume of gas which is used to inflate the folded air bag which moves through the aligned opening formed in the trim piece in being deployed into the passenger compartment.
There has previously been devised various arrangements for severing the covering layer, which is typically constructed of relatively tough vinyl plastic.
In U.S. Pat. No. 5,080,393 issued on Jan. 14, 1992, for "METHOD AND APPARATUS FOR FORMING AN AIR BAG DEPLOYMENT OPENING"; U.S. Pat. No. 5,217,244 issued on Jun. 8, 1993, for "ARRANGEMENT FOR FORMING AN AIR BAG DEPLOYMENT OPENING"; U.S. Pat. No. 4,991,870 issued on Feb. 12, 1991, for "METHOD AND ARRANGEMENT FOR FORMING AN AIR BAG DEPLOYMENT OPENING IN AN AUTO INTERIOR TRIM PIECE" there are described various pyrotechnic linear energy generating elements which cause a severing of the covering layer by the energy released by activation of a pyrotechnic or other chemical reaction, either by direct or indirect application of the released energy.
U.S. Pat. No. 5,082,310 issued on Jan. 21, 1992, for an "ARRANGEMENT FOR PROVIDING AN AIR BAG DEPLOYMENT OPENING" describes a mechanical cutting edge driven by the air bag inflation to sever the covering layer.
In U.S. application Ser. No. 08/210,503, filed on Mar. 18, 1994, for "Method and Arrangement for Forming an Air Bag Deployment Opening", now abandoned in favor of copending continuing application Ser. No. 08/279,225, filed on Jul. 22, 1994, there is described a flattened tube which is rapidly expanded by discharge of a pyrotechnic material, the expansion of the tube used to drive various cutting edge arrangements to execute cutting of the covering layer.
In those arrangements using a separate source of energy from the air bag inflation, a critical consideration is the need to initiate the cutting action at a sufficient interval before air bag inflation but after the system deployment sequence is initiated.
Another important consideration is the assembly and handling of a separate energy generating element, particularly where the element must generate sufficient energy to itself sever the covering layer.
Accordingly, it is an object of the present invention to provide an improved instrument panel or air bag assembly having an integral arrangement for severing a covering layer overlying an air bag receptacle in which assembly and handling of a linear element used to sever the covering layer is simplified.
It is a further object to provide such an arrangement in which the components necessary to insure properly timed activation are simplified.